This invention relates to electric circuit making and breaking contact arrangements of the current limiting type. More specifically, the invention relates to a current limiting contact arrangement which incorporates an arc transfer structure for assisting interruption of the electrical arc. The contact arrangement of this invention is particularly well suited for use in electric circuit breakers of the type which afford overcurrent protection.
Electric circuit breakers of the aforemention type comprise separable contacts which may be selectively operated between open and closed positions by a manual operator. In addition, such circuit breakers comprise current sensing structures which operate thermal and magnetic trip mechanisms to automatically trip the contacts open upon sensing currents that are in excess of predetermined amounts. The thermal sensing apparatus operates to trip the contacts open upon sensing currents which exceed a predetermined value by a first magnitude whereas the magnetic sensing means operates to trip the contacts open upon sensing currents in excess of a predetermined value of a second, greater magnitude. Increased current levels being made available by electric utility companies have introduced a still greater third magnitude of overcurrents which the electric circuit breaker is required to interrupt to provide the desired protection to the branch circuit and electric apparatus connected to that branch circuit. To interrupt currents which exceed the predetermined value by such third magnitude, circuit breaker designs incorporate current limiting contacts which generally comprise a pair of contacts and contact supports arranged to provide oppositely directed spaced parallel current paths whereby high currents generate repelling electromagnetic forces between the two contact structures to force the contacts apart independently of the thermal or magnetic trip mechanism. Such current limiting contact separation occurs faster than the magnetic trip structure can respond and causes the contacts to separate with great speed. A resulting electrical arc drawn between the contacts can sustain current flow and it is therefore also important to rapidly extinguish or break the arc. This invention relates to current limiting contact structures having improved arc extinguishing capabilities.